Electronics > KiCad

Managing equivalent units (for example for 74xx logic)

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berke:
Hi all,

I have a bunch of logic gates (74xx series NAND, NOR) and I didn't pay much attention when capturing the schematic, so I have too many ICs as I'm only using one IC per gate!  I can edit the annotation and the units by hand, but is there a better, less tedious way?

(Yes, I did search the forum with terms such as "merging kicad logic"...)

I'm using KiCad 6.0.6.

langwadt:
wouldn't you want to do it by hand anyway?

they might not all have the same voltage, you wouldnt' want to route across the whole board or to the opposite side of a chip if swapping makes it much easier, etc.

berke:

--- Quote from: langwadt on July 29, 2022, 10:53:29 am ---wouldn't you want to do it by hand anyway?

they might not all have the same voltage, you wouldnt' want to route across the whole board or to the opposite side of a chip if swapping makes it much easier, etc.

--- End quote ---

They're all the same but valid point for routing.  That's what I ended up doing anyway.  For posterity here is the workflow :

- Generate a BOM and look at the collated components section, say you have 8 7400's
- Go over each gate
  - Press E to edit the IC number, use the first available
  - Select the unit (A,B,C then D)
  - When done move to the next unit
- There will be gaps in the IC numbering, so reannotate

Yes during layout I may have to do pin/gate/IC swapping.

retiredfeline:

--- Quote from: berke on July 29, 2022, 11:18:53 am ---- There will be gaps in the IC numbering, so reannotate

--- End quote ---

There is no problem with having gaps in the numbering, but if they bother you, do as you please. I sometimes take advantage of gaps, for example, the left channel of an amplifier might have components 1xx, and the corresponding ones on the right 2xx.

julian1:
One tip. Drop all the symbols Units on a schematic, whenever a new part is added. That way you can visually see what logic is used/available for routing at any time.

It is preferable to do this anyway to ensure nothing is forgotten, and that any unused input is tied off to avoid oscillation/floating pins. I think DRC sometimes fails to check this condition.

Otherwise, maybe you can work out the high-level routing on paper first.

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